Why are my glass reflections so far apart?
The problem is that the Mix node using the 'is Reflection Ray' is causing the glass to behave as a single refractive surface - which doesn't exist in the 'real' world. Normally the refraction would bend the light one way on entering a solid and the other way on exiting the solid, effectively cancelling each other out.

However, I believe the Mix node is resulting in rays entering the glass and being refracted as normal, reflecting off the back surface of the glass, and then passing out of the front surface of the glass without refracting back the other way.

In order to demonstrate this, change the color of the Glass Shader to give the light that passes through it a tint to make it identifiable to that reflected off the surface. Also, increase the IOR to make its effect more pronounced. You should get something like the following :



As you can see, the 'untinted' reflection is the same as that on the surface of the other pane. This is not passing through the glass and is not refracting - it is simply the reflection off the surface of the glass.

The 'tinted' reflection is entering the glass and reflecting off the back surface. However, it is not being refracted at both surfaces - only one since the Mix is causing the surface to behave as Transparent on one transition - and this is causing it to act as a lens.